Could it be that Penn's appeal is tied to him being one of the best actors of his generation?

Or is it that the thespian, who honed his craft on the stages of New York before heading to Hollywood, is not afraid of taking on new roles, even if that requires gruelling training to get a physique like Sylvester Stallone?

Penn is following in the geriatric action hero footsteps of Liam Neeson for The Gunman, which opens here tomorrow.

It is a genre the two-time Oscar winner has not touched since Sydney Pollack's The Interpreter in 2005, though the latter is not even on the same level as the actioner The Gunman is.

In the latest movie, he plays a former assassin-turned-humanitarian worker whose last job - killing a politician from the Democratic Republic of Congo - comes back to haunt him.

Directed by Pierre Morel, the Frenchman behind Neeson's Taken movies, it sees Penn sharing some intimate scenes with stunning Italian actress Jasmine Trinca. It is a sight that is disconcerting, because we are so accustomed to seeing a serious Penn on screen.

So the question remains: Why do hot babes dig him?

REFORMED BAD BOY

Women fall for the type our mothers warned us about.

Ever since Penn broke out playing spaced-out surfer dude Jeff Spicoli in Fast Times At Ridgemont High (1982), he earned his "bad boy" reputation for being the leather-clad actor who rode motorbikes, fell out with directors and co-stars and who lashed out at the paparazzi.

He even served 33 days of a 60-day solitary confinement jail sentence in 1987 for violating probation he was given for punching a fan who had tried to get too close to ex-wife Madonna.

Their tumultuous marriage was tainted with domestic violence. He reportedly struck her across the head with a baseball bat in 1987.

The couple ended their four-year union in 1989, but are now on friendly terms.

His second marriage, to Wright in 1996, also ended in divorce, although this time it lasted 14 years.

Although both parties have been reluctant to talk about their split, there was supposedly much sadness.

Some say Wright's career was overshadowed by Penn's fame, while Penn told Esquire in 2012 that he "didn't feel loved".

He admitted to Esquire UK that he was led by two things in his life - rage and influence. But he is said to have mellowed, particularly after hooking up with Theron last year.

Theron, who has been outspoken about gun violence after experiencing it first-hand at 17 when her mother shot and killed her father in self-defence, inspired Penn to melt down his prized 65-gun collection.

It was turned into a sculpture by US artist Jeff Koons.

HUMANITARIAN

Penn is hands-on when it comes to charity work.

When Hurricane Katrina hit the Gulf coast of the US in 2005, he travelled to New Orleans and was personally involved in rescuing dozens of flood victims.

He reportedly arrived in capital city Port-au-Prince in January 2010 in the aftermath of the Haiti earthquake with a plane full of doctors and medical supplies.

That same year, Penn founded J/P Haitian Relief Organisation, which offers construction, medical, engineering, community development and education assistance to the country.

He once told Vanity Fair: "I wanted to give back something more to help struggling people, but I didn't know how to best do it.

"I was for 20 years in a relationship with Robin and 18 years with children.

"I didn't have time to commit to anything - for real - in places like Iraq, except to denounce the war. But now I'm single. I can lend a hand."

CLOSET ROMANTIC

Penn, who has two children with Wright - daughter Dylan, 24, and son Hopper, 22 - has taken on the additional responsibility of playing daddy to Theron's adopted three-year-old son Jackson.

He has reportedly filed to legally adopt the boy.

Penn has also been uncharacteristically vocal when it comes to proclaiming his love for Theron, telling Esquire that he was surprised to find love at 53.

"To run into somebody now who you care about is a much more passionate, deeper, truer and a much happier feeling," said Penn.

"It's a lot more romantic and a lot more fulfilling to be in a relationship and to think you're a good person within it."

This article was first published on April 8, 2015. Get The New Paper for more stories.